The present invention relates to a work roll for use in the cold rolling of metals, and particularly to a quenched roll that is made of forged steel and has high grindability.
For the cold rolling of steel strips and aluminum plates, there have conventionally been used quenched work rolls made of forged steel that comprise by weight, 0.75-1.20% C, 2-5% Cr and 0.15-0.55% Mo, with Ni and V being optionally added in amounts not exceeding 2% and 0.5%, respectively (see Unexamined Published Japanese Patent Application (kokai) No. 55-100965/1980).
With the increasing requirements that have to be satisfied as to the surface properties of workpieces to be cold rolled in modern mills, the grindability of the work roll used in the rolling operation has become an extremely important factor. Stated briefly, the surfaces of work rolls that have been ground under specified conditions are required not only to be within specified roughness ranges but also to contain less than specified numbers of scratches and microscopic point flaws.
These requirements cannot be fully met by rolls having the compositional ranges specified in Unexamined Published Japanese Patent Application (kokai) No. 55-100965/1980 since it is difficult to suppress the development of scratches, as well as to finish-work the rolls to a specified roughness range in a consistent manner. In fact, neither attempting to alter the grinding conditions nor that to depend entirely upon the skill and expertise of grinding personnel has been satisfactory.
A proposal has therefore been made that these problems be solved by redesigning the material of the work roll to be used (see Unexamined Published Japanese Patent Application (kokai) No. 1-104750). A roll having the compositional ranges specified by this proposal satisfies most of the requirements for better grindability. However, the result is not completely satisfactory in areas where fine scratches caused by the grinding operation can be a serious problem, as exemplified by the cold rolling of aluminum which is to be used as a material for making presensitized offset plates. Hence, a technique that can achieve a complete improvement in this aspect has long been desired.